1. Field of the Invention
The present invention relates to a sheet handling device for feeding a sheet to a predetermined position.
2. Description of the Prior Art
In an image forming apparatus such as a copying machine, a sheet handling device for feeding an original sheet to an exposure position is usually used.
Such a sheet handling device may be a document feeder (DF) which feeds an original sheet manually set by an operator to an entry tray one by one or an automatic document feeder (ADF) which automatically feeds sheets, one at a time, which are set by the operator to a document mount. Those document feeders are in union with the copying machine. Accordingly, when it is desired to change the DF to the ADF, it is necessary to remove the DF and attach the ADF.
The ADF comprises a mechanism (AF unit) for automatically separating the original sheets one by one which are set by the operator on the document mount and a mechanism (DF unit) for feeding the separated original sheet to the exposure position.
In order to assure the separation ability in the AF unit, it is necessary to lower a feed speed of the original sheets. Thus, where the AF unit and the DF unit are driven by the same drive system, the drive speed is determined by the AF unit. As a result, an original exchange time increases, which results in a low performance of the original sheet handling device.
Further, since the separation of the next original sheet is started when the current original sheet is ejected from the DF unit after the copy operation, the original exchange time is too long and the performance of the original sheet handling device is lowered.
In a certain AF unit, the original sheets mounted on the angled original mount abut against ends of two separation belts by their gravity and one of the belts is moved in the direction of feed of the original sheet while the other belt is moved in the return direction so that one original sheet is separated from a number of original sheets. However, the separation of thin original sheets is very difficult to attain because of strong attractive force between the original sheets.
Further, in such an original sheet handling device, the original sheet may be jammed in the device in the course of feeding to the exposure positon due to skew or slip. Thus, means for informing the jam to an operator by an alarm lamp has been proposed. When the jam occurs, the operator takes out the jammed original sheet form the device and resets an output of an original sheet sensor to a no original sheet state. in such an arrangement, even if a motor is stopped when the jam occurs, the jammed original sheet is moved by an inertia and the sensor no longer senses the jam and it may be reset in spite of the jam condition.
In such a device, the original sheet taken out by the opertor can be stacked on the original sheets mounted on the document mount and the feeding can be started again. However, when the jammed original sheet is stacked on the original sheets and the feeding is started again, the original sheet is easily skewed and jammed again.
In such an original sheet handling device, where a plurality of paper ejection paths for ejecting the original sheet after the exposure operation are provided, means for checking whether the ejection was properly effected or not is required for each ejection path. When the ejection paths are of different lengths, a jam timer is to be arranged in front of each ejection path to check proper ejection accordingly, the device is very complex.